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Scientists Identify Origin And History Of H7N9 Bird Flu Virus

Published
Friday 3 May 2013 Published Fri 3 May 2013

By Joseph Nordqvist

For the first time ever, a comprehensive genetic analysis of the H7N9 bird flu virus has been carried out by scientists in China. The findings encompass the origin and evolutionary history of the virus.

The first case of the novel avian influenza A H7N9 virus was identified on March 30, 2013. By April 18 the virus had spread and was detected in six different provinces and cities in China (Shanghai, Anhui, Jiangsu, Zhejiang, Beijing, and Henan).

A H7N9 has already infected 87 people across China, of whom 17 have died.

The researchers set out to identify potential origins of the virus as well as "possible routes of reassortment events" by correlating the genomic sequences from avian influenza viruses with ecological information.

The team used the Global Initiative on Sharing Avian Influenza Data (GISAID) database to gather as much information as possible about the H7N9 virus genome sequences.

They conducted phylogenetic and coalescent analyses on 100 extracted sequences, and identified three different potential points of origin of the virus, of American, Oceanian, and Eurasian lineages.

The authors wrote that the A H7N9 was genetically close to sequences found among isolated ducks in the Zhejiang Province.

They wrote: "The H7 phylogenetic tree also showed that varied H7 viruses were circulating in wild ducks along the east Asian flyway, which covers eastern China, South Korea, and Japan."

The diversity among the isolates suggests that the H7N9 virus might have evolved into two different lineages.

In conclusion, they believe that the influenza A H7N9 virus might have originated from duck avian influenza viruses as well as chicken avian influenza viruses.

The authors concluded:

"The HA and NA genes might originate from duck avian influenza viruses, which might have obtained the viral genes from migratory birds a year previously, whereas the internal genes might come from chicken avian influenza viruses.

We believe that the estimated times to most recent common ancestor for the eight genomic fragments and the frequent poultry transportation in China account for the increased number of confirmed sporadic cases of human infection. In particular, this novel H7N9 virus has diversified into different lineages since its emergence several months ago."

It is imperative that extensive global surveillance is carried out to ensure that domestic-poultry-to-person transmission is carefully watched.

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